An object to be examined, e.g. a patient, of which an X-ray image is to be acquired, is regularly arranged between an X-ray generating device, e.g. an X-ray tube, and an X-ray detector element in the path of X-ray radiation. Said X-ray radiation is penetrating the object emanating from the X-ray generating device, subsequently arriving at the X-ray detector element. An inner structure or tissue structure of the object to be examined provides a spatial attenuation of the X-ray beam arriving at the X-ray detector after passage of the object. The X-ray radiation, spatially attenuated by the object, is subsequently detected by the X-ray detector. Said attenuation information is then employed for generating X-ray image information of the object.
For obtaining said X-ray image information, an X-ray detector element is registering a photon energy and/or a photon count of photons arriving at the detector. The photon energy generates a photo current in the detector element, in particular in each pixel element of a photodetector, which is substantially read out, i.e. provided as an output of the X-ray detector to subsequent electronics or circuitry for generating said image information.
X-ray detectors may be embodied as photoconductors with ohmic contacts which output a photo current depending on the energy and amount of photons impinging on a respective photoconductor element or X-ray detector pixel element. Such photoconductors with ohmic contacts may exhibit a photoconductive gain ii, i.e. the measured current of such an X-ray detector pixel when irradiated by X-radiation is higher, possibly much higher, than the current, which would result from impinging photons only generating electron-hole pairs. The current only generated by impinging photons, which may be optical, X-ray or other types, is referred to as photo current.
U.S. Pat. No. 6,759,658 B2 describes an X-ray detector having a large dynamic range, further describing a combination of a counting and integrating channel.
WO 2007/010448 A2 describes X-ray detector imaging with polychromatic spectra, further describing a combination of a counting channel with several energy thresholds and an integrating channel.